1. Field of the Invention
This invention relates to a method for determining the number of fingers on a sensing device, more particularly to a relatively accurate method for determining the number of fingers on a sensing device.
2. Description of the Related Art
A single-finger sensing device for emulating a computer mouse is well known in the art. With the single-finger sensing device, commonly used functions, such as the click-and-drag function, are more difficult to perform than with the computer mouse. To solve this problem, it has been proposed to use a multi-finger sensing device. In U.S. Pat. No. 5,825,352, there is disclosed a conventional method for determining the number of fingers on a sensing device that has a plurality of scanlines. As illustrated in FIG. 1, the sensing device 1 has a plurality of scanlines 11 (only one of the scanlines 11 is shown in FIG. 1). The conventional method includes the steps of:
A) defining a maximum value 10 , and a minimum value 20 less than the maximum value 10;
B) when the number of detecting signals 101 generated by the scanline 11 of the sensing device 1 is one and when the detecting signal 101 has a maxima that is not less than the maximum value 10, determining the number of the fingers 30 on the sensing device 1 to be one;
C) when the number of the detecting signals 101, 102 generated by the scanline 11 of the sensing device 1 is two and when only one of the detecting signals 101 has a maxima that is not less than the maximum value 10, determining the number of the fingers 30 on the sensing device 1 to be one; and
D) when the number of the detecting signals 101, 102 generated by the scanline 11 of the sensing device 1 is two, when each of the detecting signals 101, 102 has a maxima that is greater than the maximum value 10, and when a minima between the detecting signals 101, 102 is less than the minimum value 20, determining the number of the fingers 30 on the sensing device 1 to be two.
The aforementioned conventional method is disadvantageous in that, as illustrated in FIG. 2, it is incapable of distinguishing between a detecting signal 101 generated by a scanline 11 when the corresponding scanline 11 detected a finger 30 and a detecting signal 100 generated by a scanline 11 due to a noise on the corresponding scanline 11.